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Linux KernelOperating system · Linux

CVE-2026-31533

CRITICAL · 9.8 CVSS v3.1 Published 2026-04-23
Fix available
A fix is available. Upgrade to 5.15.203 / 6.1.169 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: net/tls: fix use-after-free in -EBUSY error path of tls_do_encryption The -EBUSY handling in tls_do_encryption(), introduced by commit 859054147318 ("net: tls: handle backlogging of crypto requests"), has a use-after-free due to double cleanup of encrypt_pending and the scatterlist entry. When crypto_aead_encrypt() returns -EBUSY, the request is enqueued to the cryptd backlog and the async callback tls_encrypt_done() will be invoked upon completion. That callback unconditionally restores the scatterlist entry (sge->offset, sge->length) and decrements ctx->encrypt_pending. However, if tls_encrypt_async_wait() returns an error, the synchronous error path in tls_do_encryption() performs the same cleanup again, double-decrementing encrypt_pending and double-restoring the scatterlist. The double-decrement corrupts the encrypt_pending sentinel (initialized to 1), making tls_encrypt_async_wait() permanently skip the wait for pending async callbacks. A subsequent sendmsg can then free the tls_rec via bpf_exec_tx_verdict() while a cryptd callback is still pending, resulting in a use-after-free when the callback fires on the freed record. Fix this by skipping the synchronous cleanup when the -EBUSY async wait returns an error, since the callback has already handled encrypt_pending and sge restoration.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In the Linux kernel's TLS implementation, a race condition exists where the async callback tls_encrypt_done() and the synchronous error path in tls_do_encryption() both attempt to clean up encrypt_pending and restore scatterlist entries when crypto_aead_encrypt() returns -EBUSY. This double-cleanup corrupts the encrypt_pending sentinel, causing subsequent sendmsg operations to free tls_rec while a pending cryptd callback still references it, resulting in a use-after-free vulnerability.

MitigationApply the kernel update containing the fix for commit that resolves the double-cleanup in tls_do_encryption(). If immediate patching is not possible, consider disabling TLS crypto async operations or restricting TLS usage until the patch can be deployed.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 5.15.160, < 5.15.203>= 6.1.84, < 6.1.169>= 6.6.18, < 6.6.135>= 6.7.6, < 6.8>= 6.8.1, < 6.12.82>= 6.13, < 6.18.23>= 6.19, < 6.19.13= 7.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed kernel version
    Run `uname -r` or `cat /proc/version` to get the kernel version
    Affected if The version falls within any of these ranges: >= 5.15.160 and < 5.15.203; >= 6.1.84 and < 6.1.169; >= 6.6.18 and < 6.6.135; >= 6.7.6 and < 6.8; >= 6.8.1 and < 6.12.82; >= 6.13 and < 6.18.23; >= 6.19 and < 6.19.13; = 7.0
  2. Verify Kernel TLS support is available
    Check if the tls module is loaded with `lsmod | grep tls` or verify TLS crypto algorithms are registered in `/proc/crypto`
    Affected if Kernel TLS (ktls) support is loaded or built into the kernel, enabling the vulnerable code path in tls_do_encryption()
  3. Check for TLS handshake activity using async encryption
    Monitor kernel logs and TLS connection state. The vulnerability triggers when crypto_aead_encrypt() returns -EBUSY, indicating the async cryptd callback path is used
    Affected if The system is actively processing TLS connections where the kernel crypto API returns -EBUSY, forcing use of the async path where the double-cleanup bug occurs

You are affected if your kernel version is in the affected list AND Kernel TLS support is enabled and actively processing TLS connections that trigger the async encryption error path.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.15.203 / 6.1.169 / 6.6.135 or later
Fixed in 5.15.2036.1.1696.6.135
Vendor patch git.kernel.org →
Interim mitigation

Apply the kernel update containing the fix for commit that resolves the double-cleanup in tls_do_encryption(). If immediate patching is not possible, consider disabling TLS crypto async operations or restricting TLS usage until the patch can be deployed.

Recommended fix High confidence

Upgrade to kernel version 5.15.203 or later for 5.15.x, 6.1.169 or later for 6.1.x, 6.6.135 or later for 6.6.x, or 6.8 or later for 6.7.x

  1. 1. Identify the currently running Linux kernel version using `uname -r`
  2. 2. Check if the running version is one of the affected versions: 5.15.160-5.15.202, 6.1.84-6.1.168, 6.6.18-6.6.134, or 6.7.6-6.7.x
  3. 3. If affected, plan for a system reboot after upgrading the kernel
  4. 4. For Debian/Ubuntu: Update package lists with `apt update` and install the new kernel package with `apt install linux-image-<version>` where version is the fixed release (e.g., 5.15.203, 6.1.169, 6.6.135, or 6.8+)
  5. 5. For RHEL/CentOS: Use `yum update kernel` or `dnf update kernel` to install the fixed kernel version
  6. 6. For other distributions: Obtain the kernel source from https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git, apply commit 02f3ecadb23558bbe068e6504118f1b712d4ece0, compile and install the custom kernel
  7. 7. After installation, reboot the system to load the fixed kernel
  8. 8. Verify the fix is applied by checking the kernel version with `uname -r` and confirming it meets or exceeds the fixed releases: >= 5.15.203, >= 6.1.169, >= 6.6.135, or >= 6.8
Caveat Kernel upgrades may require system reboot and could have compatibility implications with custom kernel modules or specific hardware drivers; test in staging environment before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation8.0 h
  • Implementation12.0 h
  • Testing16.0 h
  • Review / QA4.0 h
40.0 hours of engineering $6,880
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

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Peer-ranked notes from engineers who’ve handled CVE-2026-31533 in production — separate from our analysis above.

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